Techniques have long been known for depositing substances, such as layers of semiconductor material, using a plasma that is formed into a jet. For example, U.S. Pat. Nos. 4,471,003 and 4,487,162 disclose arc jet plasma deposition equipments which utilize a plasma for deposition of semiconductors and other materials. Ions and electrons are obtained by injecting an appropriate compound, such as a silicon compound, into an arc region, and a jet (or beam) is formed by utilizing magnetic fields to accelerate and focus the plasma. In recent years, equipment of this type has been used to deposit synthetic diamond. Superior physical and chemical properties make diamond desirable for many mechanical, thermal, optical and electronic applications, and the ability to deposit synthetic diamond by plasma jet deposition holds great promise, particularly if plasma jet techniques can be improved for this and other purposes. A plasma containing hydrocarbon radicals and atomic hydrogen can be obtained using electrical arcing, and the resultant plasma focused and accelerated toward a substrate so that polycrystalline diamond film is deposited on the substrate. Reference can be made, for example, to U.S. Pat. No. 5,204,144, assigned to the same assignee as the present Application, for description of an example of a type of plasma jet deposition that can be utilized to deposit synthetic diamond on a substrate.
In various commercial applications it is desirable to have relatively large size diamond films. In plasma jet deposition techniques there are various factors which limit the practical size of the deposition area that is active on a substrate at a particular moment. For example, when an arc is employed to generate the heated gas mixture in an arc jet plasma deposition system, the diameter of the beam can be limited by a number of factors. Since the cross-section of the plasma beam is generally limited in practical applications, the area on which it is desired to deposit a diamond film may be larger than the deposition beam. This means that it may be desirable to move the beam and the target substrate with respect to each other during the deposition process. This has been achieved by spinning the substrate during deposition, which helps to promote temperature uniformity over the substrate, as well as to attain larger area substrate coverage (see e.g. the referenced U.S. Pat. No. 5,204,144). Reference can also be made to U.S. Pat. Nos. 5,342,660, 5,435,849, 5,487,787, and 5,551,983, and to U.S. patent application Ser. No. 08/480,580.
In the typical DC plasma assisted CVD diamond deposition process, a DC arc jet is used to produce activated species of gases, often atomic hydrogen and hydrocarbons. These activated species are caused to flow over a substrate which is maintained at appropriate conditions of temperature and pressure to foster the deposition of polycrystalline diamond film. The percentage of the activated gas species that is engaged into the actual deposition process at the substrate surface is called the capture efficiency. This percentage is often quite low, such as under 50%, particularly when a single flat substrate surface is used. In such cases, much of the activated gas species does not flow directly over the deposition surface, but is lost as overspray, diverted over the sides of the substrate, or does not penetrate the gas boundary layer which covers the substrate surface and hence is not available to participate in the actual film deposition process.
A second problem with single flat substrates is the non-uniformity of thickness of the deposited film, due to non-uniform gas conditions over the entire area of the substrate. Uniformity can be improved by methods such as those described in the above-referenced U.S. Patents and Application. There are limits, however, to the size of single diamond films which can be properly deposited because the properties of the gas change as the relative amounts of atomic hydrogen and activated carbon species in the plasma beam are depleted by deposition and by losses. For similar reasons, the relative quality of the deposited film is also subject to variation across the diameter (or linear dimension) of the substrate. Particularly, the amount and relative percentage of atomic hydrogen in the gas mixture tends to decrease as the gas continues to flow across the deposition surface. This can result in a undesirable change in the quality and growth rate of the diamond material.
It is among the objects of the present invention to provide improvements in plasma beam deposition of diamond film. It is also among the objects of the present invention to provide improved substrate arrays and techniques using such arrays in diamond film deposition.